Former CIA Director John Brennan says he warned Russia against meddling in the U.S. election in an August call to the head of the Russian intelligence service. (May 23, 2017) (Sign up for our free video newsletter here)

Former CIA Director John Brennan says he warned Russia against meddling in the U.S. election in an August call to the head of the Russian intelligence service. (May 23, 2017) (Sign up for our free video newsletter here)

Greg MillerWashington Post

The CIA alerted the FBI to a troubling pattern of contacts between Russian officials and associates of the Trump campaign last year, former agency director John Brennan testified on Tuesday, shedding new light on the origin of a criminal probe that now reaches into the White House.

In testimony before the House Intelligence Committee, Brennan said he became increasingly concerned that Donald Trump associates were being manipulated by Russian intelligence services as part of a broader covert influence campaign that sought to disrupt the election and deliver the presidency to Trump.

"I was worried by a number of the contacts that the Russians had with U.S. persons," Brennan said, adding that he did not see proof of collusion before he left office on Jan. 20, but "felt as though the FBI investigation was certainly well-founded and needed to look into those issues."

Brennan's remarks represent the most detailed public accounting to date of his tenure as CIA director during the alleged Russian assault on the U.S. presidential race, and the agency's role in triggering an FBI probe that Trump has sought to contain.

"It should be clear to everyone that Russia brazenly interfered in our 2016 presidential election process," Brennan said at one point, one of several moments in which his words seemed aimed squarely at the president.

Trump has refused to fully accept the unanimous conclusion of U.S. intelligence agencies that Russia stole thousands of sensitive emails, orchestrated online dumps of damaging information and employed fake news and other means to upend the 2016 race.

GOP lawmakers spent much of Tuesday's hearing trying to get Brennan to concede that he had no conclusive evidence of collusion between the Trump campaign and Moscow. Brennan acknowledged that he still had "unresolved questions" about the purpose of those contacts when he stepped down as CIA director in January.

But, "I know what the Russians try to do," Brennan said. "They try to suborn individuals and they try to get individuals, including U.S. persons, to act on their behalf either wittingly or unwittingly."

Brennan refused to name any of the U.S. individuals who were apparently detected communicating with Russian officials. The FBI investigation, which began last July, has scrutinized Trump associates including Paul Manafort, Trump's former campaign manager; Carter Page, who was once listed as a foreign policy adviser to Trump; and former national security adviser Michael Flynn, who was forced to resign after misleading statements about his contacts with the Russian ambassador were exposed.

The probe has intensified in recent weeks and identified a current White House official as a significant person of interest.

Because Russia uses intermediaries and other measures to disguise its hand, "many times, [U.S. individuals] do not know that the individual they are interacting with is a Russian," Brennan said.

He added that Russian agencies routinely seek to gather compromising information, or "kompromat," to coerce treason from U.S. officials who "do not even realize they are on that path until it gets too late." The remark appeared to be in reference to Flynn.

The Senate Intelligence Committee is issuing two new subpoenas for information from Flynn's companies and challenging his lawyer's refusal to comply with an existing subpoena for documents detailing his contacts with Russian officials, committee leaders announced Tuesday.

"A business does not have the right to take the Fifth," Sen. Mark R. Warner (Va.), the committee's lead Democrat, told reporters as he and Chairman Richard Burr (R-N.C.) pledged to "keep all options on the table."

Brennan was also asked about Trump's disclosure of highly classified information to the Russian foreign minister and ambassador in a White House meeting this month. Brennan said that the CIA at times provided tips about terrorist plots to the Kremlin, but he indicated that Trump violated key protocols.

Sensitive information should only be passed through intelligence services, not divulged to foreign ministers or ambassadors, Brennan said. Referring to the information revealed by Trump, Brennan said it had neither gone through "the proper channels nor did the originating agency have the opportunity to clear language for it."

Brennan was a key figure in the Obama administration's handling of Russian election interference. As alarm grew, Brennan held classified meetings with top congressional officials in the fall to impress upon them the unprecedented nature of Moscow's interference.

Later, Brennan was among the top officials who briefed then-President-elect Trump on the scale of Russia's intervention, and its assessed goal of helping Trump win.

On Tuesday, Brennan testified that he was the first to confront a senior member of the Russian government on the matter, using an August phone conversation with the head of Russia's security service, the FSB, to warn that the meddling would backfire and damage the country's relationship with the United States.

Brennan said he told FSB chief Alexander Bortnikov that "American voters would be outraged by any Russian attempt to interfere in the election" and that such activity "would destroy any near-term prospect of improvement" in relations with the United States.

Bortnikov twice denied that Russia was waging such a campaign, according to Brennan, but said he would carry the message to Russian President Vladimir Putin.

"I believe I was the first U.S. official to brace Russia on this matter," Brennan said.

The Obama administration went on to issue statements publicly accusing Moscow of election meddling, and in December announced punitive measures including the expulsion of 35 suspected Russian intelligence operatives from the United States.

Despite those warnings and efforts at retaliation, Brennan said that Russia was probably not dissuaded from attempting similar interference operations in the future.

The former CIA chief is the latest senior Obama administration official to appear publicly before Congress in hearings that have often produced damaging headlines for Trump.

Earlier this month, former acting attorney general Sally Yates testified that she expected White House officials to "take action" after warning that Flynn had misled administration officials about his contacts with Russia.

At that same hearing, former director of national intelligence James Clapper Jr. said that Moscow's leaders "must be congratulating themselves for having exceeded their wildest expectations with a minimal expenditure of resource," a reference not only to the outcome of the 2016 race but also to the chaos that has characterized the early months of the Trump administration.

Brennan has feuded publicly with Trump over the president's treatment of intelligence agencies. In January, he lashed out at Trump for comparing U.S. spy agencies with Nazi secret police.

Brennan was particularly offended by Trump's remarks during a speech at CIA headquarters on the day after he was inaugurated. Trump used the CIA's Memorial Wall - a collection of engraved stars marking the lives of agency operatives killed in the line of duty - to launch a rambling speech in which he bragged about his election victory.

Brennan called the appearance "despicable" and said that Trump should be "ashamed."